1. Field of the Invention
The present invention relates generally to control mechanisms and, more particularly, to a servo-mechanism employing an internal model coordination feedforward method.
2. Description of the Prior Art
In control mechanisms, particularly servo-mechanisms, it is indispensable to utilize an internal model principle in order to improve the capability of a controlled value to follow up a desired value or a reference value and to eliminate any steady state error as well as to reduce the influence of disturbances upon the controlled variable, thereby, for example, eliminating steady state errors due to disturbances. (Refer to B. A. Francis, The Multivariable Servo Mechanism Problem from the Input-Output Viewpoint, IEEE Trans. Automatic Control, AC-22-3,322/328 (1977).) Deadbeat control, optimal control, adaptive control, repetitive control and the like are known as typical control methods. Each of these control methods has a different feature, and is applied to suitable portions of various control mechanisms to achieve the objects thereof. Also, a general-purpose and standard method of setting controllers and regulators in each of these control mechanisms which involves the utilization of the internal model principle is regarded as having been substantially established, and it is deemed that the designs of many kinds of control mechanisms, particularly designs based on current control theories, have started with the above-described established method. Also, control mechanisms utilizing feedforward systems are widely used, and they are applied to individual systems in a suitable applied form. In addition, a new method is proposed. (Refer to, for example, Jiaqing Wang and Takeshi Tsuchiya, Minimal Order Output Feedback Control System Design Method with Feedforward Control Loops and its Application, the transaction of the institute of electrical engineers of Japan, Paper C, Volume 105, No. 5, 93/100, 1985.)
However, the history of development of current control theories is relatively new, and it is relatively recently that they have been applied to actual control mechanisms owing to improvements in the performance of various kinds of computers and the miniaturization thereof as well as an increased diffusion of computers as a result of a reduction in price.
Current control mechanisms including internal models comprise, in addition to regulators responsible for feedback of the state variables of controlled systems, gain controllers which are set similar to the regulators so as to receive the state variables of the respective internal models as new state variables. Thus, the current control mechanisms are constructed to produce a manipulation variable as an amplified corollary of the state variables, thereby enabling satisfactory control. However, since the constituent elements of many of the internal models are integrators or similar devices, there is still the problem in terms of the quickness of response with respect to abrupt changes in a desired value or a reference value. However, it does not seem that a general-purpose method which can solve such a problem, and which is one development of the prior art methods of setting controllers and regulators, has been intensively studied.
There is a possibility that new, superior and general-purpose methods can be found as one development of such prior art methods, and it is considered that a further improvement should be pursued through the improvement of the quickness and dispersibility of response, reductions in manipulation variables and the lessening of the influence of disturbance. To this end, it has been proposed to provide one method utilizing feedforward (refer to the above document). However, this proposal has been made as a "by-product" of difficult theoretical analyses, and therefore the resultant systems are difficult to achieve because of their complicated constructions. In a situation in which each form of feedforward must be utilized for a different kind of control, no general-purpose method has been proposed.